I don't think that's really an issue, Ilyn. Skills get changed every expac. Assassinate back in Stormblood was a...40s? CD that you could only use when the boss was below 20% HP. Then it became a combo action from DWAD that was a guaranteed CDH. And now DWAD is an upgrade to it. These types of changes happen every cycle and the potency that Assassinate has will be spread among other actions or put onto new ones. It wasn't even a powerful CDH hit, base 200 potency when stuff like Machinist's Reassembled Drill or Warrior's IR Fell Cleaves actually benefitted from it, Hyosho Ranryu is much more satisfying to land.

You're also complaining about something that's a major part of the job, Ninjutsu. Why would Ninja not use Ninjutsu? 'Everything is Ninjutsu' for NIN like 'everything is jumps' for DRG or 'everything is everything is summons' for new Summoner. It's not currently bare while levelling and it still won't be, the only part of the current rotation that actually got removed is Shadow Fang which isn't even that engaging to begin with, you press it once a minute under Huton or once every 70s before level 45. The levelling experience is there to teach you how to play a job and what each button does, the game has to assume that any job can be the first job a player levels and has to be prepared for that fact.